Heavy fluid injection method for cellar hydrocarbon recovery

ABSTRACT

A method for producing residual hydrocarbon located in a cellar region of a reservoir after SAGD hydrocarbon production, wherein a higher-density fluid is injected into a first producer well to displace the residual hydrocarbon toward a second, adjacent producer well. The method may also produce residual hydrocarbon located in infill regions.

FIELD OF THE INVENTION

The present invention relates to hydrocarbon recovery methods, and more specifically to methods for recovering residual hydrocarbon located in a cellar region of a reservoir after SAGD hydrocarbon production.

BACKGROUND OF THE INVENTION

It is known in the art of hydrocarbon recovery, and particularly in the recovery of heavy hydrocarbons from subsurface reservoirs, to employ the use of steam or steam-solvent mixtures as an injectant to reduce the viscosity of the hydrocarbon and allow it to flow to a producing well and thereby be produced to surface. For example, cyclic steam stimulation (CSS) and steam-assisted gravity drainage (SAGD) methods employ steam to mobilize subsurface hydrocarbon such as heavy oil or bitumen.

SAGD involves a pair of horizontal wells that are drilled into a hydrocarbon reservoir. The upper wellbore is typically referred to as the injector well, while the lower wellbore may be referred to as the producer well. In a SAGD hydrocarbon recovery operation, high pressure steam is continuously injected into the upper wellbore to heat the hydrocarbon and reduce its viscosity. The heated hydrocarbon drains into the lower wellbore as a result of gravity. The resulting hydrocarbon in the lower producer wellbore may be pumped to surface.

However, there may be regions in a reservoir that contain hydrocarbon, including mobilized hydrocarbon, that was not recovered during SAGD operations. For example, the cellar region is generally below a producing well and an infill region is a region between adjacent SAGD well pairs. Both these regions are potential sources of residual hydrocarbon within a reservoir after SAGD operations have ceased.

What is needed, therefore, is a method to produce the hydrocarbon from such non-depleted regions after SAGD operations have occurred.

SUMMARY OF THE INVENTION

The present invention therefore seeks to provide a method for producing residual hydrocarbon located in a cellar region, and possibly infill regions, of a reservoir after SAGD hydrocarbon production.

According to a first broad aspect of the present invention, there is provided a method for producing residual hydrocarbon located in a cellar region of a reservoir after SAGD hydrocarbon production, the method comprising the steps of:

-   -   a. drilling a first SAGD well pair into the reservoir,         comprising a first injector well and a first producer well;     -   b. drilling a second SAGD well pair into the reservoir,         comprising a second injector well and a second producer well,         adjacent the first SAGD well pair;     -   c. operating the first and second SAGD well pairs to produce         hydrocarbon from the reservoir, leaving the residual hydrocarbon         in the cellar of the reservoir;     -   d. ceasing production of the hydrocarbon through the first         producer well;     -   e. injecting a fluid into the reservoir through one of the first         injector well and the first producer well, the fluid having a         density greater than the density of the residual hydrocarbon;     -   f. allowing the residual hydrocarbon to be displaced from the         cellar toward the second producer well by the injecting of the         fluid; and     -   g. producing the residual hydrocarbon through the second         producer well.

The method according to the first broad aspect of the present invention may also comprise the step, after step d. but before step e., of injecting steam through the first injector well or the first producer well to condition the reservoir. Optionally, an acid may be added to the fluid before injection, to reduce liner scaling.

The fluid may be a brine solution. The fluid may be heated before injection. Furthermore, electrical cables may be placed in the first injector well or the first producer well to apply in-situ heat to the fluid during injection into the reservoir. Optionally, steam may be injected with the fluid.

The method according to the first broad aspect of the present invention may further comprise the step of using vacuum insulated tubing to retain heat in the fluid prior to the fluid entry into the reservoir.

The method according to the first broad aspect of the present invention may further comprise the step of using inflow control devices on the first injector well or the first producer well to control fluid injection locations.

In some exemplary embodiments of the first aspect, the method may further comprise the step of producing infill hydrocarbon from between the first and second SAGD well pairs while producing the residual hydrocarbon.

According to a second broad aspect of the present invention, there is provided a method for producing residual hydrocarbon located in a cellar region of a reservoir after SAGD hydrocarbon production, the method comprising the steps of:

-   -   a. drilling a first SAGD well pair into the reservoir,         comprising a first injector well and a first producer well;     -   b. drilling a second SAGD well pair into the reservoir,         comprising a second injector well and a second producer well,         adjacent the first SAGD well pair;     -   c. drilling a third SAGD well pair into the reservoir,         comprising a third injector well and a third producer well, such         that the first SAGD well pair is situated between the second         SAGD well pair and the third SAGD well pair;     -   d. operating the first, second and third SAGD well pairs to         produce hydrocarbon from the reservoir, leaving the residual         hydrocarbon in the cellar of the reservoir;     -   e. ceasing production of the hydrocarbon through the first         producer well;     -   f. injecting a fluid into the reservoir through one of the first         injector well and the first producer well, the fluid having a         density greater than the density of the residual hydrocarbon;     -   g. allowing the residual hydrocarbon to be displaced from the         cellar toward the second and third producer wells by the         injecting of the fluid; and     -   h. producing the residual hydrocarbon through the second and         third producer wells.

The method according to the second broad aspect of the present invention may also comprise the step, after step e. but before step f., of injecting steam through the first injector well or the first producer well to condition the reservoir. Optionally, an acid may be added to the fluid before injection, to reduce liner scaling.

The fluid may be a brine solution. The fluid may be heated before injection. Furthermore, electrical cables may be placed in the first injector well or the first producer well to apply in-situ heat to the fluid during injection into the reservoir. Optionally, steam may be injected with the fluid.

The method according to the second broad aspect of the present invention may further comprise the step of using vacuum insulated tubing to retain heat in the fluid prior to the fluid entry into the reservoir.

The method according to the second broad aspect of the present invention may further comprise the step of using inflow control devices on the first injector well or the first producer well to control fluid injection locations.

In some exemplary embodiments of the second aspect, the method may further comprise the step of producing infill hydrocarbon from between the first and second SAGD well pairs and from between the first and third SAGD well pairs while producing the residual hydrocarbon.

According to a third broad aspect of the present invention, there is provided a method for displacing residual hydrocarbon located in a cellar region of a reservoir after SAGD hydrocarbon production, the method comprising the steps of:

-   -   a. drilling and operating a first SAGD well pair comprising a         first injector well and a first producer well, and a second SAGD         well pair comprising a second injector well and a second         producer well, leaving the residual hydrocarbon in the cellar of         the reservoir;     -   b. ceasing production through the first producer well;     -   c. injecting a fluid into the reservoir through one of the first         injector well and the first producer well, the fluid having a         density greater than the density of the residual hydrocarbon;     -   d. allowing the residual hydrocarbon to be displaced by the         fluid from the cellar toward the second producer well; and     -   e. producing the residual hydrocarbon through the second         producer well.

The method according to the third broad aspect of the present invention may also comprise the step, after step b. but before step c., of injecting steam through the first injector well or the first producer well to condition the reservoir. Optionally, an acid may be added to the fluid before injection, to reduce liner scaling.

The fluid may be a brine solution. The fluid may be heated before injection. Furthermore, electrical cables may be placed in the first injector well or the first producer well to apply in-situ heat to the fluid during injection into the reservoir. Optionally, steam may be injected with the fluid.

The method according to the third broad aspect of the present invention may further comprise the step of using vacuum insulated tubing to retain heat in the fluid prior to the fluid entry into the reservoir.

The method according to the third broad aspect of the present invention may further comprise the step of using inflow control devices on the first injector well or the first producer well to control fluid injection locations.

In some exemplary embodiments of the third aspect, the method may further comprise the step of producing infill hydrocarbon from between the first and second SAGD well pairs while producing the residual hydrocarbon.

A detailed description of exemplary embodiments of the present invention is given in the following. It is to be understood, however, that the invention is not to be construed as being limited to these embodiments. The exemplary embodiments are directed to a particular application of the present invention, while it will be clear to those skilled in the art that the present invention has applicability beyond the exemplary embodiments set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate exemplary embodiments of the present invention:

FIG. 1 is a simplified elevation view of a first exemplary embodiment comprising two well pairs; and

FIG. 2 is a simplified elevation view of a second exemplary embodiment comprising three well pairs.

Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Throughout the following description specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. The following description of examples of the technology is not intended to be exhaustive or to limit the invention to the precise form of any exemplary embodiment. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

The present invention is directed to methods for producing residual hydrocarbon located in a cellar region, and optionally also in infill regions. Specifically, the methods are for use with SAGD wells after ceasing production of hydrocarbon using conventional SAGD methods.

The present invention involves the injection of a fluid with a greater density than the residual hydrocarbon in the cellar region, after SAGD operations have ceased. The fluid is injected into either a first injector well or a first producer well, which then displaces cellar region hydrocarbon toward an adjacent second producer well where it is produced to surface.

Turning to FIG. 1, a first embodiment of the present invention is illustrated. Two adjacent SAGD well pairs 102, 108 are shown as present in a reservoir 100 situated between a caprock 116 and a basement layer 118, each of the well pairs 102, 108 comprising an injector well 104, 110 and a producer well 106, 112 in a conventional arrangement. A steam chamber region 114 has formed due to conventional operation of the SAGD well pairs 102, 108, within the reservoir 100 and below the caprock 116. In a lower part of the reservoir 100, a cellar region 120 forms below the steam chamber 114 which may contain residual hydrocarbon after SAGD operations have ceased, including hydrocarbon that may have been mobilized by the SAGD operations. Due to formation of the steam chamber 114, the producer wells 106, 112 are unable to access the residual hydrocarbon in the cellar region 120, and such residual hydrocarbon is commonly left unproduced in prior art methods. There is also an infill region 122 between the adjacent well pairs 102, 108 that may also contain residual hydrocarbon after SAGD operations have ceased, due to steam chamber 114 formation, which again may go unproduced to some extent in conventional operations.

The method illustrated in FIG. 1 begins with drilling the two adjacent SAGD well pairs 102, 108, and then operating them using conventional SAGD methods to produce hydrocarbon from the reservoir 100. After the SAGD operations have ceased and the steam chamber 114 has formed, residual hydrocarbon remains in the cellar region 120 and the infill region 122. A fluid 124 is then illustrated as being injected into the reservoir 100 through the first producer well 106, although it will be clear that the fluid 124 could alternatively be injected through the first injector well 104. The fluid 124 is selected to have a density greater than the density of the residual hydrocarbon in the cellar region 120. Preferably, the fluid 124 is a brine solution having a density greater than the density of the residual hydrocarbon in the cellar region 120. The fluid 124 injected through the first producer well 106 displaces the residual hydrocarbon that is in the cellar region 120 toward the second producer well 112. Once in the second producer well 112, the residual hydrocarbon can be produced to surface via methods known in the art. A person skilled in the art would know of hydrocarbon production methods suitable for application to embodiments of the present invention. As the fluid 124 displaces the lighter residual hydrocarbon from the cellar region 120, the fluid 124 itself remains in the cellar region 120, and is a low value material that does not need to be produced to surface.

The method according to the embodiment of FIG. 1 may further comprise displacement of residual hydrocarbon from the infill region 122 toward the second producer well 112. Similarly to the displacement of residual hydrocarbon from the cellar region 120, the fluid 124 injected through the first producer well 106 may displace the residual hydrocarbon that is in the infill region 122 toward the second producer well 112 where it can be produced to surface via methods known in the art.

Turning now to FIG. 2, a second embodiment of the present invention is illustrated. In this illustrated embodiment, three adjacent SAGD well pairs 202, 208, 226 are shown as present in a reservoir 200 situated between a caprock 216 and a basement layer 218, each of the well pairs 202, 208, 226 comprising an injector well 204, 210, 228 and a producer well 206, 212, 230 in a conventional arrangement. The first well pair 202 is situated between the second well pair 208 and the third well pair 226. A steam chamber region 214 has formed due to conventional operation of the SAGD well pairs 202, 208, 226, within the reservoir 200 and below the caprock 216. In a lower part of the reservoir 200, cellar regions 220 a, 220 b form below the steam chamber 214 which may contain residual hydrocarbon after SAGD operations have ceased, including hydrocarbon that may have been mobilized by the SAGD operations. Due to formation of the steam chamber 214, the producer wells 206, 212, 230 are unable to access the residual hydrocarbon in the cellar regions 220 a, 220 b, and such residual hydrocarbon is commonly left unproduced in prior art methods. There are also infill regions 222 a, 222 b between the adjacent well pairs 202, 208, 226 that may also contain residual hydrocarbon after SAGD operations have ceased, due to steam chamber 214 formation, which again may go unproduced to some extent in conventional operations.

The method illustrated in FIG. 2 begins with drilling the three adjacent SAGD well pairs 202, 208, 226 and then operating them using conventional SAGD methods to produce hydrocarbon from the reservoir 200. After the SAGD operations have ceased and the steam chamber 214 has formed, residual hydrocarbon remains in the cellar regions 220 a, 220 b and the infill regions 222 a, 222 b. A fluid 224 is then illustrated as being injected into the reservoir through the first producer well 206, although the fluid 224 may alternatively be injected through the first injector well 204. The fluid 224 is selected to have a density greater than the density of the residual hydrocarbon in the cellar regions 220 a, 220 b. Preferably, the fluid 224 is a brine solution having a density greater than the density of the residual hydrocarbon in the cellar regions 220 a, 220 b. The fluid 224 injected through the first producer well 206 displaces the residual hydrocarbon that is in the cellar regions 220 a, 220 b toward the second and third producer wells 212, 230. Once in the second and third producer wells 212, 230, the residual hydrocarbon can be produced to surface via methods known in the art. A person skilled in the art would know of hydrocarbon production methods suitable for application to embodiments of the present invention. As the fluid 224 displaces the lighter residual hydrocarbon from the cellar regions 220 a, 220 b, the fluid 224 itself remains in those regions 220 a, 220 b, and is a low value material that does not need to be produced to surface.

The method according to the embodiment of FIG. 2 may further comprise displacement of residual hydrocarbon from the infill regions 222 a, 222 b toward the second and third producer wells 212, 230. Similarly to displacement of residual hydrocarbon from the cellar regions 220 a, 220 b, the fluid 224 injected through the first producer well 206 may displace the residual hydrocarbon that is in the infill regions 222 a, 222 b, toward the second and third producer wells 212, 230 where it can be produced to surface via methods known in the art.

The exemplary embodiments described above may also comprise other features. For example, steam may be injected through the first producer well before injection of the higher-density fluid to condition the reservoir and the well. Optionally, an acid may be added to the higher-density fluid before injection, to reduce liner scaling.

The higher-density fluid may be heated before injection. Electrical cables may also be placed in the first producer well to apply in-situ heat to the fluid during injection into the reservoir. Optionally, steam may be injected with the higher-density fluid. Vacuum insulated tubing may be used in the first producer well to retain heat in the fluid prior to the fluid entry into the reservoir.

Inflow control devices may optionally be used on the first producer well to control fluid injection locations, in a manner known to those skilled in the art.

Unless the context clearly requires otherwise, throughout the description and the claims:

-   -   “comprise”, “comprising”, and the like are to be construed in an         inclusive sense, as opposed to an exclusive or exhaustive sense;         that is to say, in the sense of “including, but not limited to”.     -   “connected”, “coupled”, or any variant thereof, means any         connection or coupling, either direct or indirect, between two         or more elements; the coupling or connection between the         elements can be physical, logical, or a combination thereof.     -   “herein”, “above”, “below”, and words of similar import, when         used to describe this specification shall refer to this         specification as a whole and not to any particular portions of         this specification.     -   “or”, in reference to a list of two or more items, covers all of         the following interpretations of the word: any of the items in         the list, all of the items in the list, and any combination of         the items in the list.     -   the singular forms “a”, “an” and “the” also include the meaning         of any appropriate plural forms.

Words that indicate directions such as “vertical”, “transverse”, “horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”, “outward”, “vertical”, “transverse”, “left”, “right”, “front”, “back”, “top”, “bottom”, “below”, “above”, “under”, and the like, used in this description and any accompanying claims (where present) depend on the specific orientation of the apparatus described and illustrated. The subject matter described herein may assume various alternative orientations. Accordingly, these directional terms are not strictly defined and should not be interpreted narrowly.

Where a component (e.g. a circuit, module, assembly, device, etc.) is referred to herein, unless otherwise indicated, reference to that component (including a reference to a “means”) should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which performs the function in the illustrated exemplary embodiments of the invention.

Specific examples of methods and apparatus have been described herein for purposes of illustration. These are only examples. The technology provided herein can be applied to contexts other than the exemplary contexts described above. Many alterations, modifications, additions, omissions and permutations are possible within the practice of this invention. This invention includes variations on described embodiments that would be apparent to the skilled person, including variations obtained by: replacing features, elements and/or acts with equivalent features, elements and/or acts; mixing and matching of features, elements and/or acts from different embodiments; combining features, elements and/or acts from embodiments as described herein with features, elements and/or acts of other technology; and/or omitting combining features, elements and/or acts from described embodiments.

The foregoing is considered as illustrative only of the principles of the invention. The scope of the claims should not be limited by the exemplary embodiments set forth in the foregoing, but should be given the broadest interpretation consistent with the specification as a whole. 

1. A method for producing residual hydrocarbon located in a cellar region of a reservoir after SAGD hydrocarbon production, the method comprising the steps of: a. drilling a first SAGD well pair into the reservoir, comprising a first injector well and a first producer well; b. drilling a second SAGD well pair into the reservoir, comprising a second injector well and a second producer well, adjacent the first SAGD well pair; c. operating the first and second SAGD well pairs to produce hydrocarbon from the reservoir, leaving the residual hydrocarbon in the cellar of the reservoir; d. ceasing production of the hydrocarbon through the first producer well; e. injecting a fluid into the reservoir through one of the first injector well and the first producer well, the fluid having a density greater than the density of the residual hydrocarbon; f. allowing the residual hydrocarbon to be displaced from the cellar toward the second producer well by the injecting of the fluid; and g. producing the residual hydrocarbon through the second producer well.
 2. The method of claim 1 further comprising the step, after step d. but before step e., of injecting steam through the one of the first injector well and the first producer well to condition the reservoir.
 3. The method of claim 1 wherein the fluid is a brine solution.
 4. The method of claim 1 wherein the fluid is heated before injection.
 5. The method of claim 4 further comprising the step of using vacuum insulated tubing to retain heat in the fluid prior to the fluid entry into the reservoir.
 6. The method of claim 1 wherein an acid is added to the fluid before injection, to reduce liner scaling.
 7. The method of claim 1 further comprising using inflow control devices on the one of the first injector well and the first producer well to control fluid injection locations.
 8. The method of claim 1 further comprising the step of producing infill hydrocarbon from between the first and second SAGD well pairs while producing the residual hydrocarbon.
 9. The method of claim 1 further comprising the step of injecting steam with the fluid.
 10. The method of claim 1 further comprising the step of placing electrical cables in the one of the first injector well and the first producer well to apply in-situ heat to the fluid during injection into the reservoir.
 11. A method for producing residual hydrocarbon located in a cellar region of a reservoir after SAGD hydrocarbon production, the method comprising the steps of: a. drilling a first SAGD well pair into the reservoir, comprising a first injector well and a first producer well; b. drilling a second SAGD well pair into the reservoir, comprising a second injector well and a second producer well, adjacent the first SAGD well pair; c. drilling a third SAGD well pair into the reservoir, comprising a third injector well and a third producer well, such that the first SAGD well pair is situated between the second SAGD well pair and the third SAGD well pair; d. operating the first, second and third SAGD well pairs to produce hydrocarbon from the reservoir, leaving the residual hydrocarbon in the cellar of the reservoir; e. ceasing production of the hydrocarbon through the first producer well; f. injecting a fluid into the reservoir through one of the first injector well and the first producer well, the fluid having a density greater than the density of the residual hydrocarbon; g. allowing the residual hydrocarbon to be displaced from the cellar toward the second and third producer wells by the injecting of the fluid; and h. producing the residual hydrocarbon through the second and third producer wells.
 12. The method of claim 11 further comprising the step, after step e. but before step f., of injecting steam through the one of the first injector well and the first producer well to condition the reservoir.
 13. The method of claim 11 wherein the fluid is a brine solution.
 14. The method of claim 11 wherein the fluid is heated before injection.
 15. The method of claim 14 further comprising using vacuum insulated tubing to retain heat in the fluid prior to the fluid entry into the reservoir.
 16. The method of claim 11 wherein an acid is added to the fluid before injection, to reduce liner scaling.
 17. The method of claim 11 further comprising the step of using inflow control devices on the one of the first injector well and the first producer well to control fluid injection locations.
 18. The method of claim 11 further comprising the step of producing infill hydrocarbon from between the first and second SAGD well pairs and from between the first and third SAGD well pairs while producing the residual hydrocarbon.
 19. The method of claim 11 further comprising the step of injecting steam with the fluid.
 20. The method of claim 11 further comprising the step of placing electrical cables in the one of the first injector well and the first producer well to apply in-situ heat to the fluid during injection into the reservoir.
 21. A method for displacing residual hydrocarbon located in a cellar region of a reservoir after SAGD hydrocarbon production, the method comprising the steps of: a. drilling and operating a first SAGD well pair comprising a first injector well and a first producer well, and a second SAGD well pair comprising a second injector well and a second producer well, leaving the residual hydrocarbon in the cellar of the reservoir; b. ceasing production through the first producer well; c. injecting a fluid into the reservoir through one of the first injector well and the first producer well, the fluid having a density greater than the density of the residual hydrocarbon; d. allowing the residual hydrocarbon to be displaced by the fluid from the cellar toward the second producer well; and e. producing the residual hydrocarbon through the second producer well.
 22. The method of claim 21 further comprising the step, after step b. but before step c., of injecting steam through the one of the first injector well and the first producer well to condition the reservoir.
 23. The method of claim 21 wherein the fluid is a brine solution.
 24. The method of claim 21 wherein the fluid is heated before injection.
 25. The method of claim 24 further comprising the step of using vacuum insulated tubing to retain heat in the fluid prior to the fluid entry into the reservoir.
 26. The method of claim 21 wherein an acid is added to the fluid before injection, to reduce liner scaling.
 27. The method of claim 21 further comprising using inflow control devices on the one of the first injector well and the first producer well to control fluid injection locations.
 28. The method of claim 21 further comprising the step of producing infill hydrocarbon from between the first and second SAGD well pairs while producing the residual hydrocarbon.
 29. The method of claim 21 further comprising the step of injecting steam with the fluid.
 30. The method of claim 21 further comprising the step of placing electrical cables in the one of the first injector well and the first producer well to apply in-situ heat to the fluid during injection into the reservoir. 